1. Field of the Invention
The present invention relates generally to methods and systems for the treatment of myopia progression. In particular, the present invention relates to methods and systems for treating myopia progression in myopic patients who also exhibit near point esophoria, esophoria at near, eso fixation disparity, and/or eso associated phoria.
Myopia, also known as nearsightedness, is a visual defect in which distant objects appear blurred because their images are focused in front of the retina rather than on it causing a retinal blur. Myopia is one of the more prevalent human visual disorders, affecting up to 25% of American adults, with associated cost of correction and management having been estimated at several billion dollars per year. In some regions of the world, up to 75% of people may have myopia. Moreover, the prevalence of myopia may even be increasing. In some instances, high levels of myopia may result in grave consequences, such as, blindness from retinal detachment, myopic macular degeneration, cataract, glaucoma, or severe side effects or complications from myopia correction. Thus, treatments which control, reduce, inhibit, or even reverse myopia progression would have a widespread benefit.
It is believed that myopia may be caused by environmental factors, particularly intensive and excessive near work, with hereditary/genetic factors further defining susceptibility. Numerous animal studies have demonstrated that prolonged hyperopic defocus triggers an increase in eye growth, typically along an axial length of the eye, which can cause myopic change, as shown in FIG. 1. The dotted line in FIG. 1 denotes expansion of the eye, particularly the vitreous body by growth of the choroid and/or sclera. Prolonged hyperopic defocus may be caused by naturally occurring refractive errors. More importantly, people engaged in intense near work while in a state of inadequate accommodation (i.e. accommodation deficiencies during near work tasks) often encounter hyperopic defocus. Both accommodation deficiencies and life styles or occupations involving intensive near work result in frequent exposure to hyperopic defocus which in turn induces myopia. It has further been reported in several studies that larger than normal xe2x80x9caccommodative lagsxe2x80x9d have been measured in progressing myopes. The term xe2x80x9caccommodative lagsxe2x80x9d refers to hyperopic accommodative errors during intensive near work.
A number of techniques have been developed over the years to control or prevent myopia progression. These techniques include rigid contact lenses, spectacles, pharmacological delivery of atropine, biofeedback, vision training, and intentional undercorrection. Surgical correction of myopia includes refractive surgery, including myopic keratomileusis, radial keratotomy, and photorefractive keratotomy. While all these techniques have enjoyed varying levels of success, no one of these procedures is proven to provide significant myopia progression reduction or prevention in all cases.
Of particular interest to the present invention is the relationship of decreased accommodation to esophoria at near in defining the causes of progressive myopia. The term xe2x80x9cesophoriaxe2x80x9d refers to a tendency of the eyes to turn inward. About 25% of myopic people have this eye crossing tendency. In particular, near esophoria or near point esophoria may cause decreased accommodation of the eyes during near work tasks, increasing accommodation lag. This may induce hyperopic defocus and ocular growth and thus drive myopia progression. Alternatively, decreased accommodative response may be compensated by convergence accommodation which in turn causes esophoria.
Several studies have suggested the use of bifocal spectacles or glasses to reduce the rate of myopia progression in near point esophoric children. While these proposals appear promising, they have not provided the desired evidence of myopia progression control. Moreover, the use of bifocal spectacles suffer from several inherent disadvantages that may limit their effectiveness in myopia control. For example, bifocal power is often avoided or improperly used by children (e.g. not lowering their gaze to read through the bifocal power or raise their chin to view a computer screen through the bifocal power) as well as the fact that bifocal spectacles do not provide coverage for all angles of view.
In light of the above, it would be desirable to provide improved methods and systems for the treatment of myopia progression. In particular, it would be desirable to provide improved methods and systems for controlling myopia progression in near point esophoric myope patients with a significant level of success. It would be further desirable if such treatment methods could not be avoided or used incorrectly by the patient and provide sufficient coverage for all angles of view. At least some of these objectives will be met by the invention described hereinafter.
2. Description of Background Art
Myopia progression control using bifocal contact lenses is described in a poster abstract by T. A. Aller and D. Grisham in Optometry and Vision Science, Vol. 77, No. 12s, Poster 92, page 182 (December 2000). Bifocal spectacle control of myopia progression in children with nearpoint esophoria is described by Goss et al. in Optometry and Vision Science, 67:637-640 (1990) and Goss et al. in Journal of Optometric Vision Development, 30:25-32 (1999). Progressive spectacles in slowing myopia is described by Leung et al. in Optometry and Vision Science, 76:346-54 (1999). An editorial by J. T. Barr in Contact Lens Spectrum, August (1999) speculates on the use of soft bifocal contact lenses for treating myopes. U.S. Pat. No. 6,045,578 describes the use of contact lenses to alter a degree of spherical aberration stop or slow myopia. U.S. Pat. No. 5,838,419 describes a method for treating myopia by altering the spectral distribution of incident light on the eye by filter or tints provided on contact lenses. U.S. Pat. Nos. 5,695,509 and 3,760,807 describe optical molds applied as hard contact lenses to reshape a surface of the cornea to reverse myopia.
The full disclosures of each of the above references are incorporated herein by reference.
The present invention provides new methods and systems for treating myopia progression in myopic patients who also exhibit near point esophoria, esophoria at near, eso fixation disparity, and/or eso associated phoria by selectively prescribing bifocal (soft or rigid gas permeable) contact lenses to such patients. In particular, the myopigenic effects of accommodation lag during intensive near work and hyperopic defocus are addressed by treating patients who also suffer from near point esophoria. The present invention further provides a significant level of success in controlling myopia progression in esophoric myopes through the prescription of bifocal contact lenses. Bifocal contact lenses advantageously allow for effective myopia progression control as most bifocal contacts act on the principal of simultaneous vision where add powers are available independent of gaze. As such, it is less likely that a bifocal contact lens patient can avoid use of the bifocal power or otherwise use it incorrectly. Moreover, bifocal contact lenses provide sufficient coverage for all angles the eye may scan.
In a first aspect, the present invention provides methods for selectively prescribing bifocal contact lenses for controlling myopia progression. One method comprises identifying a myopic patient who exhibits near point esophoria, eso fixation disparity, or eso associated phoria, measuring an amount of fixation disparity, and prescribing a bifocal contact lens add power prescription. The bifocal near power prescription is based on the fixation disparity measurement and the bifocal distance prescription is based upon a distance prescription of the patient""s eye.
Common ophthalmic measurements, such as alternating cover test, Van Graefe phoria test, Maddox rod phoria test, Titmus vision screening, vectographic fixation disparity tests, anaglyphic fixation disparity tests, telebinocular vision screening tests, computer-based tests, and like optometric tests allow for identification of near point xe2x80x9cesophoricxe2x80x9d patients. The term xe2x80x9cesophoricxe2x80x9d referring to an eye crossing tendency. Patients preferably exhibit esophoria at near as measured through their full distance correction. Most patients who are near point esophoric further have the inability to control this eye crossing tendency, thus exhibiting eso fixation disparity or eso associated phoria. Near point eso fixation disparity may include esophores, low exophores, and orthophores.
Refractive criteria, such as identification of myopia, may be based on ophthalmic measurement protocols, such as subjective history, visual acuity testing, retinoscopy, automated objective refraction, subjective refraction, cycloplegic refraction, wavefront analysis, and like optometric tests. Myopic patients may exhibit at least xe2x88x920.5 D myopia in the least myopic meridian and myopia progression of at least xe2x88x920.25 D in either principal meridian in either eye in the past year. It should be noted that myopia progression rates are sometimes difficult to gauge due to inconsistent measurement protocols, seasonal variations in near work activity, etc. However, it is most likely that myopic esophoric patients are progressing myopes due to observed associations between near point esophoria and myopia progression. The refractive criteria may further include identification of patients with anisometropia less than 2 D as anisometropia greater than 2 D may lead to increased risks of binocular instability and/or amblyopia. Patients with an astigmatism less than 1.5 D may further be identified. The treated patients may be pre-presbyopic, typically patients under 40 years of age, to prevent having patient that previously used reading glasses or bifocals for standard reasons relating to age. It will be appreciated, however, that the above described refractive criteria may not limit the efficacy or effectiveness of the present invention. For example, astigmatism in amounts greater than 1.5 D may affect clarity of vision with soft bifocal contact lenses, but could be well corrected for by rigid gas permeable bifocals or soft bifocal astigmatism correcting lenses. Moreover, patients with anisometropia greater than 2 D and progressing esophoric myopes over the age of 40 may still benefit from the protocols of the present invention.
Measuring fixation disparity comprises determining an amount of actual crossing of the patient""s eyes. Fixation disparity measurements are typically made by viewing a displaced polarized image, such as polarized lines or arrows that are vertically or horizontally displaced, through a phoropter or trial glasses having a polarized filter, aligning the polarized image, and detecting a degree of vertical and/or horizontal misalignment of the patient""s eyes based on a difference between the aligned image and true alignment. For a more detailed discourse concerning polarization techniques, reference is made to the following publications which are incorporated herein by reference: Mallett, R. F. J., A Fixation Disparity Test for Distance Use, The Optician, (July 1966) and Mallett, R. F. J., The Investigation of Heterphoria at Near and a New Fixation Disparity Technique, The Optician, (December 1966). Alternative devices and techniques used to measure fixation disparity include measuring an amount of prism or a power of an ophthalmic lens required to eliminate the fixation disparity. This is typically known as the associated phoria. Still further, alternative devices to measure fixation disparity may include the use of red or green filters instead of the Polaroid filters. The bifocal contact lens power prescription is then prescribed based on the fixation disparity measurement and a straight prescription for the patient""s eye. The straight prescription is based on correcting refractive criteria, such as the amount of myopia or nearsightedness. The use of bifocal contact lenses in controlling myopia progression is particularly advantageous as the bifocal power prescription is tailored to maximally reduce the amount of near point esophoria. Specifically, the bifocal power prescription takes into account how much bifocal power is needed to correct actual eye crossing or fixation disparity.
The bifocal contact lens prescription will vary for each patient as it is ideally tailored to reduce or inhibit esophoria at near. The reduction or inhibition of esophoria at near with the bifocal contact lens power prescription may decrease accommodative lag as well as hyperopic defocus. This reduction in hyperopic defocus may result in less myopia progression. As such, the bifocal contact lens prescription may reduce accommodation lag and/or hyperopic defocus which in turn may result in reduction of myopia progression. Hence, the myopigenic effects of accommodation lag during intensive near work and hyperopic defocus may be altered by bifocal contact lenses that correct fixation disparity. Ocular growth associated with myopia progression may further be reduced with the bifocal contact lens prescription. The present methodology corrects fixation disparity with bifocal power adjustments until the patient sees straight so as to reduce myopia progression. It is further a treatment goal that the bifocal contact lens prescription preferably provide distance visual acuity of at least 20/30 in both eyes, most preferably corrected visual acuity of 20/20 in both eyes.
The present invention further provides a significant level of success in controlling myopia progression in esophoric myopes through the prescription of bifocal contact lenses. In particular, the bifocal contact lens power prescription reduces myopia progression to preferably less than xe2x88x920.2 D per year, more preferably to less than xe2x88x920.08 D per year. The rate of myopia progression may be reduced by 70%, preferably by 80%, most preferably by 90% with the bifocal contact lens power prescription. The bifocal contact lens power prescription may in certain circumstances inhibit or even reverse myopia progression.
The bifocal contact lens add power prescription may significantly reduce myopia progression for late onset myopes. In particular, bifocal contact lenses may reduce myopia progression for those over the age of 20 to a greater degree than for those under the age of 20. This difference based on age is consistent with the theory that late onset myopia is associated with intensive near work. Thus, the use of bifocal contact lenses that alter the stresses caused by intense near work through the correction of fixation disparity will cause more progression reduction for adults than children. However, it will be appreciated that both children and adults may benefit from the prescription of bifocal contact lenses to reduce myopia progression. The bifocal contact lens power prescription is further effective at all prescription or diopter levels of myopia.
The bifocal contact lenses preferably comprises simultaneous vision or coaxial/concentric bifocals that provide add power in all fields of gaze. The bifocal contact lens preferably comprises a soft contact lens. In certain circumstances, the bifocal contact lens may comprise a hard contact lens, a rigid gas permeable contact lens, or an intraocular or intrastromal lens. The bifocal contact lenses may further provide high oxygen permeability to prevent against any cornea swelling. Bifocal contact lenses that may be suitable for use in the present invention may be obtained from a number of bifocal contact lens manufacturers including Bausch and Lomb, Johnson and Johnson, Unilens, Ciba, Coopervision, Ultravision, Sunsoft, and the like. Preferably, Acuvue bifocal contact lenses having add powers in the range from +1.00 to +2.50 and supplied from Johnson and Johnson will be employed in the present invention. In some instances, bifocal add power may be provided by temporarily reshaping the cornea through the use of rigid lens molds or by permanently reshaping the cornea through the use of an excimer laser to create a bifocal cornea.
In another aspect of the present invention, methods for selectively prescribing bifocal contact lenses for controlling myopia progression comprise identifying a near point esophoric myopic patient, measuring an amount of fixation disparity, prescribing a bifocal contact lens add power prescription based on the fixation disparity measurement and a distance prescription for the patient""s eye, and correcting fixation disparity with bifocal add power adjustments until the patient sees straight so as to reduce myopia progression.
In still another aspect of the present invention, systems for controlling myopia progression may be provided. The system may comprise a fixation disparity measurement device, such as those described above, a plurality of alternatively selectable bifocal contact lenses having differing add power prescriptions, and a correlation indicating a myopia progression inhibiting prescription from among the differing add power prescriptions of bifocal contact lenses in response to a reading of the fixation disparity measurement. The correlation may be simply calculated on pen and paper by an optometrist or ophthalmologist or may alternatively be carried out by a computer system.
A further understanding of the nature and advantages of the present invention will become apparent by reference to the remaining portions of the specification and drawings.